Engineering Wonders of the World
Volume III

206 ENGINEERING WONDERS OF THE WORLD, pansion engines with Corliss valve gear. These last deliver 12,000,000 gallons each per diem ; the Worthington and the marine type units have a daily duty of about 10,000,000 gallons each. It may be noted that the “ Prince Consort ” and the three “ triples ” deliver water direct into the service mains, and not, as is usually the case, into a service reservoir. The speed of the engine is governed by the rate at which the water is drawn from the main. If the demand ceased altogether, the engine, which is designed to pump against a head of about 107 feet, would stop. Near the “ Prince Consort ” is a well, 11 feet in diameter and 200 feet deep. Through the chalk to which it reaches, horizontal headings have been driven in several directions. Their total length is about 1| miles. When the supply of river water is low, as sometimes happens in the dry season, this well is requi- sitioned. As many as 3,000,000 gallons have been raised from it by the twin pumps in a day. Crossing over the Lee and the Hackney cut, we find a solitary Cornish engine, the “ Vic- toria,” delivering water to the Mile End, Strat- ford, Hackney, and other East- ern districts. In this case a standpipe, 4 feet in diameter, 120 feet high, and open at the top, serves to absorb variations in pressure— the water rising in the pipe during the delivery stroke of the pump, and sinking again during the suction stroke. The same system is used for the other two Cornish engines. Where the head of water is such that a standpipe of sufficient height cannot be provided conven- iently, a large air chamber, mounted on the main, is employed to provide the requisite “ buffering.” Among the machinery are two Girard water Turbines turbines, working two sets of three plunger pumps. They are driven by the fall of water over an adja- The Big Well. Standpipes and Air Chambers. The Walthamstow Reservoirs. by casting up cent weir in flood time. There are also two Hercules turbines driving four pumps for delivering water direct into the mains. In connection with the Lee Bridge pump- ing station should be mentioned the group of reservoirs at Walthamstow. There are twelve reservoirs in all, with a total area of 479 acres and a ca- pacity at high-water level of 2,400,000,000 gallons. Six of them contain islands—formed part of the earth excavated from the sites— planted with flowering shrubs, limes, and willows. These islands are a beautiful feature of the landscape. The reservoirs are fed by water from the Lee, and from two wells. One of the two pumping stations delivers water to reservoirs at Hornsey Wood and Haggar Lane; the other pumps to Ferry Lane and into the open aqueduct which connects the reservoirs with the Lee Bridge station. A few words about the mains which dis- tribute the water. Their aggregate length is at present about 6,280 miles. In internal diam- eter they range from 54 inches to 2 inches. There are about ^a^er Mains. 71 miles of the 54-inch mains, as many of 48- inch ; 108 miles of 36-inch ; 84 j of 24-inch ; 285 of 12-inch ; and 3,000 miles of 4-inch, which diameter is most widely employed for the smaller mains. The3-inch pipes take second place with about 1,050 miles. Tf to the mains were added the lead piping for the house services, the total mileage would be somewhat astonishing. The very moderate average of three yards of lead piping for each, man, woman, and child gives 21,000 miles ; so that we may safely assume that the pipes used for the water supply of Greater London would suffice to encircle the earth. The greatest pressures fall on the pumping mains, which in one case have to withstand a head of 600 feet.